Injection Molding
2 views
Coaxiality out of tolerance of general-purpose polyethylene injection molded products
Problem Phenomenon
The axes of the inner and outer circles or different shaft sections of the product do not coincide, and the coaxiality exceeds the tolerance requirements.
Coaxiality out of tolerance affects the dynamic balance and fitting accuracy of rotating parts, and is common in tubular products and stepped shaft products.
Cause Analysis
（1）The mold core is eccentric or the core shifts during injection, resulting in uneven wall thickness
（2）The gate position is improper, and single-side feeding generates lateral force that pushes the core off
（3）The mold temperature is uneven, and the temperature difference between the core and the cavity is large, resulting in asymmetric shrinkage
（4）The holding pressure is uneven, and the feeding on each side of the cavity is inconsistent
（5）The product structure is asymmetric, and the cooling shrinkage difference is large
Solution
（1）Check the positioning accuracy of the core, and control the coaxiality of the core and the cavity within 0.02mm
（2）Optimize the gate position, use symmetrical multi-point gates, and reduce the eccentric force of single-side feeding
（3）Control the temperature of the core and the cavity uniformly, and the temperature difference should not exceed 5°C (within the range of 30-80°C)
（4）Optimize the holding pressure scheme to ensure uniform feeding in all directions
（5）Design the product as symmetrically as possible, avoiding eccentric structures
Key Takeaway
Coaxiality out of tolerance is caused by core shift or asymmetric shrinkage, and needs to be solved from mold accuracy, gate symmetry, and temperature uniformity.
Was this helpful?
0 people found this helpful
Thank you for your feedback!